Background Optical coherence tomography angiography (OCTA) provides not only visualisation but also quantitative measurement of foveal avascular zone (FAZ). Media opacity is common in elderly subjects with cataracts. This study aimed to investigate the impact of media opacity on automated and manual FAZ measurement.
Methods Cirrus 5000 OCTA and Triton OCTA were used to image FAZ using a 3×3 mm scanning protocol from 30 eyes of 30 healthy normal subjects. Media opacity was simulated with neutral-density filters (optical density (OD): 0.10–0.48 in Cirrus 5000 and 0.15–0.51 in Triton). Signal strength (SS) and signal strength intensity (SSI) were provided by the built-in software in Cirrus 5000 and Triton, respectively. FAZ area, perimeter and circularity were measured automatically using the built-in software as well as a customised MATLAB program. FAZ metrics were also measured manually. The correlations between the OD, SS/SSI and FAZ metrics were analysed using Spearman correlation.
Results Increased OD significantly correlated with decreased SS/SSI (rs =−0.602 and −0.925, respectively, both p<0.001), decreased automated FAZ area (rs =−0.344 and −0.766, respectively, both p<0.001), but increased manual FAZ area in both Cirrus 5000 and Triton (rs =0.423 and 0.543, respectively, both p<0.001). Similar results were found for FAZ perimeter and circularity. There was a positive correlation between SS/SSI with the automated FAZ area but negative correlation with the manual FAZ area.
Conclusions The effect of media opacity on quantitative measurement of FAZ is different between automated and manual measurements. Cautions must be taken when interpreting FAZ measurement in eyes with media opacity.
- Diagnostic tests/Investigation
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Contributors JZ conducted the study and drafted the manuscript. FYT analysed the images. CC revised the manuscript. XC analysed the images. HC designed the study and revised the manuscript.
Funding This study is supported by the Grant for Key Disciplinary Project of Clinical Medicine under the Guangdong High-level University Development Program (002-18119101) and the Intramural grant of Joint Shantou International Eye Center (19-004).
Competing interests None declared.
Patient consent Obtained.
Ethics approval The study adhered to the tenets of the Declaration of Helsinki and was approved by the Ethics Review Board of Joint Shantou International Eye Center of Shantou University and the Chinese University of Hong Kong.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Data are available upon reasonable request.